There has conventionally been proposed a technique of estimating the pitch angle of a vehicle on the basis of plural images that are captured at different times by an image pickup section provided at the vehicle (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2012-026992). In this technique, on the basis of the aforementioned plural images, a translation vector that expresses the moving direction of the aforementioned image pickup section, and a rotation matrix that expresses the angle change amounts in the pitch direction of the posture of the aforementioned image pickup section, are computed.
Further, in this technique, on the basis of the direction of the aforementioned translation vector, first estimated pitch angle values are successively computed, and, by integrating the angle change amounts expressed by the aforementioned rotation matrix, second estimated pitch angle values are computed. Then, in this technique, an estimated value of the pitch angle of the vehicle is determined by correcting the second estimated pitch angle values in accordance with the deviation between the average value of the first estimated pitch angle values and the average value of the second estimated pitch angle values in a predetermined time period.